The present disclosure relates to a head related transfer function generation apparatus, a head related transfer function generation method, and a sound signal processing apparatus which are suitable, for example, to be applied to a television apparatus that adjusts a sound image position of a sound reproduced by a mounted speaker.
Up to now, in a television apparatus or an amplifier apparatus or the like that is connected to the television apparatus, one utilizing a technology called virtual sound image localization for virtually localizing a sound source of a reproduced sound at a desired position has been proposed.
This virtual sound image localization is for virtually localizing a sound image at a previously supposed position, for example, when sounds are reproduced by left and right speakers and the like arranged in the television apparatus, and to be more specific, the virtual sound image localization is realized through the following technique.
For example, a case is supposed in which stereo signals in left and right channels are reproduced by the left and right speakers arranged in the television apparatus.
As illustrated in FIG. 1, first, a head related transfer function is measured in a predetermined measurement environment. To be more specific, microphones ML and MR are installed at locations (measurement point positions) in the vicinity of both ears of a listener. Also, speakers SPL and SPR are arranged at positions where the virtual sound image localization is desired to be realized. At this time, the speaker is an example of an electro-acoustic transduction unit, and the microphone is an example of an acousto-electric transduction unit.
Then, in a state in which a dummy head DH (or which may be a human being, in this instance, a listener itself) exists, first, for example, sound reproduction of an impulse is carried out by the speaker SPL in one channel, for example, in the left channel. Then, the impulse emitted by the sound reproduction is picked up by each of the microphones ML and MR to measure a head related transfer function for the left channel. In the case of this example, the head related transfer function is measured as an impulse response.
At this time, as illustrated in FIG. 1, the impulse response serving as the head related transfer function for the left channel includes an impulse response HLd where a sound wave from the speaker SPL is picked up by the microphone ML (hereinafter, which will be referred to as impulse response of a left main component) and an impulse response HLc where a sound wave from the speaker SPL is picked up by the microphones MR (hereinafter, which will be referred to as impulse response of a left cross talk component).
Next, sound reproduction of an impulse is similarly carried out by the speaker SPR in the right channel, and the impulse emitted by the sound reproduction is picked up by each of the above-mentioned microphones ML and MR. Then, a head related transfer function for the right channel, in this instance, an impulse response for the right channel is measured.
At this time, the impulse response serving as the head related transfer function for the right channel includes an impulse response HRd where a sound wave from the speaker SPR is picked up by the microphones MR (hereinafter, which will be referred to as impulse response of a right main component) and an impulse response HRc where a sound wave from the speaker SPR is picked up by the microphone ML (hereinafter, which will be referred to as impulse response of a right cross talk component).
Then, the television apparatus convolves the impulse response of each of the head related transfer function for the left channel and the head related transfer function for the right channel as it is by applying a sound signal processing on the sound signal supplied to each of the left and right speakers.
That is, the television apparatus convolves the head related transfer function for the left channel obtained through the measurement, that is, the impulse response HLd of the left main component and the impulse response HLc of the left cross talk component with respect to the sound signal in the left channel as it is.
Also, the television apparatus convolves the head related transfer function for the right channel obtained through the measurement, that is, the impulse response HRd of the right main component and the impulse response HRc of the right cross talk component with respect to the sound signal in the right channel as it is.
With this configuration, although the sound reproduction is carried out by the left and right speakers, for example, in the case of the left and right two-channel stereo sounds, the television apparatus can realize the sound image localization (virtual sound image localization) as if the sound reproduction is carried out by left and right speakers installed at desired positions in front of the listener.
In this manner, in the virtual sound image localization, the head related transfer function in a case where the sound waves output from the speakers at desired positions are picked up by the microphones at desired positions is measured in advance, and the head related transfer function is set to be convolved to the sound signals.
Incidentally, in a case where the head related transfer function is measured, an acoustic characteristic of the speaker or the microphone itself affects the relevant head related transfer function. For this reason, even when the sound signal processing is applied on the sound signals by using the above-mentioned head related transfer function, the television apparatus may not realize the sound image localization at the desired positions in some cases.
In view of the above, as the head related transfer function measurement method, a method of normalizing a head related transfer function obtained in a state in which the dummy head DH or the like exists by a transfer pristine state characteristic in a state in which the dummy head DH or the like does not exist is proposed (for example, see Japanese Unexamined Patent Application Publication No. 2009-194682 (FIG. 1)).
According to this head related transfer function measurement method, it is possible to eliminate the acoustic characteristic of the speaker or the microphone itself, and a highly accurate sound image localization can be obtained.